G71 repeat final pass.

[PHDesigns]

Why does my lathe (Wia SKY21, Fanuc oi-TD)run 2 last roughing passes at the same number, cuts zero stock?

 

[VTM]

you'll probably have to post the code before anyone attempts to answer that for you.

 

[Mtndew]

Why does my lathe (Wia SKY21, Fanuc oi-TD)run 2 last roughing passes at the same number, cuts zero stock?

Because that's what your program tells it to do.

 

[PHDesigns]

X2.525 Z.05;
G71 U.1;
G71 P101 Q102 U.015 W0. F.012;
N101 G0 X2.343 Z.05;
G1 Z-3.38;
X2.5;
N102 G1 X2.6;
G0 Z1. M9;
G00 G28 U0.
It takes 2 passes at 2.358.
Finish is line by line.

 

[barratt]

If I'm understanding you correctly-
There is a parameter that controls this behaviour.
On a type 2 canned cycle there is no need to run a final cut as it does not leave steps.

Using a type 1 canned cycle you do need this extra pass to get rid of the steps.

Unfortunately I don't know the parameter for your control.

 

[litlerob1]

If you really want to understand why, read this Thread or any of the 5000 Threads about G71;;https://www.practicalmachinist.com/vb/cnc-machining/g70-g71-lathe-canned-cycles-354693/

But if you just want to get around it, change the U value in the first line to anything less than .0835.

 

[PHDesigns]

If you really want to understand why, read this Thread or any of the 5000 Threads about G71;;https://www.practicalmachinist.com/vb/cnc-machining/g70-g71-lathe-canned-cycles-354693/

But if you just want to get around it, change the U value in the first line to anything less than .0835.

Reason for that change is......

 

[PHDesigns]

I removed the Z in the first line inside the cycle. Took the extra pass away.

 

[litlerob1]

I removed the Z in the first line inside the cycle. Took the extra pass away.

You removed "Z.05" and it went away?? That'd be a new one for me.

The reason .0835 or less, is 2.525-(2.343+.015)=.167/2=.0835

 

[sinha]

I removed the Z in the first line inside the cycle. Took the extra pass away.

Are you sure your observation is correct?

 

[Mtndew]

X2.525 Z.05;
G71 U.1;
G71 P101 Q102 U.015 W0. F.012;
N101 G0 X2.343 Z.05;
G1 Z-3.38;
X2.5;
N102 G1 X2.6;
G0 Z1. M9;
G00 G28 U0.
It takes 2 passes at 2.358.
Finish is line by line.

If you're only taking 1 rough cut, why even have a canned cycle?
I get it, I love canned cycles, but in this case it's not needed.

 

[PHDesigns]

G0X3.Z.1
X2.525Z.05
G71U.1
G71P101Q102U.015W0.F.012
N101G0X2.343
G1Z-3.38
X2.5
N102G1X2.6
G0Z1.M9
G00G28U0.
Z6.
M1
Here is what I am running, and it's running fine. Z.05 after the N101 removed. As for the U # going to .o835 or less, I get the half material removal part, but don't see where that number makes a diff over the U.1. Program is going to calculate it anyway, right?

 

[PHDesigns]

If you're only taking 1 rough cut, why even have a canned cycle?
I get it, I love canned cycles, but in this case it's not needed.

I am not a huge fan of can cycles in general. I watch people write programs with them and use 'generic' numbers like they don't know how to calculate anything. I am decent at editing a canned cycle and have knocked several minutes off some programs but reducing the number of rough cuts. I have mostly used cam software for my cnc stuff over the years and am trying to broaden my base. Basically being an old dog, at almost 60, wanting to learn a new trick or two

 

[SeymourDumore]

Actually, that makes sense.

Your original G71 cycle was a Type2, and as such it does make a final pass on the finished contour.
When you've removed the Z move on the N101 line, in effect you've told the control that it is now a Type 1 cycle, in which case you only get one finish pass on the contour between N101 and N102

Your profile is monotonous, therefore it does not need the Type2 cycle, so you're good.

Also to note, apparently your control uses the single line G7X definition, in which case you probably also have the I and K option to use for "roughing allowance".
I have found a few differences in motions between programs using the single line and two line cycles, and I believe one of them is the second smoothing pass with Type2.

 

[yardbird]

You can dick around with it and get it to come out of it but as to why it happens I have no clue? Essentially all your doing is changing from type 2 to type 1 roughing and for whatever reason eliminates the duplicate pass.

I've run into this on a couple jobs and typically fix it like what Rob said but I've also had jobs where it gets confused buy a specific DOC then go retarded and try to cut a complete circle where it isn't possible without jacking up both the part and the holder.

I haven't pursued it any further but I have a feeling there could be a software update available for my machine or the G71 cycle on our 0i-TD controls has a bug in it.

I'd be super interested if you have the exact same issue that I had on my machine with the roughing pass in this thread, since we both have the exact same controls.

Just for shits and giggles I'll run your code on my machine tonight when I get in and see if it does the same thing as what your seeing?

Brent

https://www.practicalmachinist.com/vb/cnc-machining/g71-please-help-what-wrong-program-343067/